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Title: The application of isostatic admittance and coherence to studies of the rheology of the continental lithosphere
Author: Francis, Susan C.
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1999
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A new detailed gravity and topographic dataset covering the Qattara Depression in Western Egypt is studied, as this topographic feature is thought to have formed by erosion and, as such, should not be associated with internal loads. A comparison of the results from this data is made with those from other point datasets for Kenya, southern UK, and Greece and the Aegean, as well as with admittance and coherence estimates determined by other workers for areas in North America, Siberia, India and Australia. Two different model variations are tested. The first involves loading at the surface and at the base of the crust, while the second allows internal loads to be positioned at much shallower levels in the crust. When the model explicitly places internal loads at the base of the crust, only the data from Egypt and Kenya can be fitted at an acceptable level and are associated with elastic thickness estimates of 19 and 23 km respectively. If loading is allowed to occur at shallower levels, then the fit between the models and the data is improved in all instances, but still only gives an acceptable fit to the Egyptian and Kenyan data. Models which include near surface loading are also correlated with elastic thickness estimates (18 km for Egypt and 14 km for Kenya). Possible explanations of the failure of the model to fit other datasets are given. The best-fit models to the Qattara data invoke a non-zero ratio of internal to external loading, indicating that contrary to the initial hypothsis, this region is affected by subsurface loads but that these may be upper crustal density variations and not necessarily related to underplating at the Moho. This analysis shows that the joint use of the admittance and coherence, when correctly applied, yields the small values of the elastic thickness of the continental lithosphere expected from thermal and seismogenic studies. Furthermore, it shows how the inclusion of near surface loading successfully models the short wavelength gravity variations, previously thought to invalidate the coherence method.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available